In a semiconductor device manufacturing process, a plasma processing apparatus is used to perform a predetermined processing on a processing target substrate, for example, a semiconductor wafer, by reacting plasma of a processing gas with the processing target substrate. Conventionally, a capacitively coupled plasma etching apparatus is frequently used for single wafer plasma etching.
In general, the capacitively coupled plasma processing apparatus includes an upper electrode and a lower electrode which are arranged in parallel within a processing container configured as a vacuum chamber, in which a semiconductor wafer is mounted on the lower electrode and a high frequency power is applied between both electrodes. Then, plasma is generated between both electrodes due to high frequency discharge of the processing gas, and a plasma processing such as, for example, etching or film formation, is performed on a surface of a substrate by the radicals or ions included in the plasma.
In general, while high density plasma is generated in the capacitively coupled plasma processing apparatus by supplying a high frequency power to the lower electrode at a low pressure, a high frequency current generated by the high frequency power tends to gather in the vicinity of the center of the lower electrode in a case where the frequency of the supplied high frequency power is raised. When the high frequency current gathers in the vicinity of the center of the lower electrode, the density of plasma generated in the processing space between the lower electrode and the upper electrode and, moreover, a process characteristic on a semiconductor wafer (e.g., an etching rate in drying etching) tend to exhibit an upwardly convex profile having a peak in the vicinity of the center of the radial direction. In order to control plasma density distribution in the processing container, a conventionally known apparatus configuration includes a magnetic field forming mechanism to form a closed-loop magnetic field so that magnetic force lines pass through a processing space in a predetermined route.
For example, Japanese Patent No. 3037848 discloses a magnetic field forming mechanism, in which a rotating magnet having a N-pole and a S-pole which are sufficiently spaced apart from each other in a horizontal direction compared with the diameter of a processing target substrate is arranged on the ceiling of a processing container, and the rotating magnet is rotated around the central axis of the processing container as a rotation center so as to form a uniform magnetic field in the horizontal direction in a processing space within the processing container. In addition, Japanese Patent No. 4107518 discloses a magnetic field forming mechanism, in which a plurality of annular electrodes is arranged concentrically to constitute an upper electrode, and a plurality of magnets is installed on the ceiling of a processing container to form a horizontal magnetic field immediately below each of the annular electrodes within the processing space.